The invention relates to a flow-forming method according to the preamble of claim 1 and to a flow-forming apparatus according to the preamble of claim 10.
In a flow-forming method according to the preamble a blank is placed on a rolling mandrel of a flow-forming machine, the blank is rotated relative to at least one flow-forming roll, the at least one flow-forming roll is infed relative to the blank and the blank is axially lengthened by the flow-forming roll and flow-formed to a workpiece.
A flow-forming method according to the preamble is known from DE-A-34 02 301. In said method radial, axial and tangential force components can be measured on the flow-forming or spinning roll. The measured values determined are used for regulating the flow-forming process.
A flow-forming apparatus according to the preamble has a rolling mandrel for receiving a workpiece, at least one flow-forming roll, a drive device for producing a rotation between the workpiece and the roll and a control device for controlling an infeed in relative manner between the rolling mandrel and the flow-forming roll.
The rolling mandrel can be driven in rotary manner and the flow-forming roll can be infed radially and/or axially to the workpiece. However, it is also possible for a flow-forming roll or a plurality of such rolls driven in rotary manner and arranged on a ring driven in rotary manner, to be radially and/or axially infed to a fixed or also rotating rolling mandrel.
Such flow-forming methods and apparatuses are known and are e.g. used for cylinder flow-forming of rotationally symmetrical precision tubular components.
These known methods are more particularly characterized by economic advantages, which is essentially due to the fact of the material saving as a result of non-cutting working, in the strain hardening of the material during working and in the considerably shortened manufacturing times compared with cutting methods. In addition, such methods make it possible to produce numerous outer circumferential shapes, e.g. contour offsets or shoulders, transition radii and conical areas.
In the case of cylinder flow-forming it is possible to obtain wall thickness tolerances of a few hundredths of a millimetre. However, the cylindrical blanks normally used generally have thickness tolerances of several tenths of a millimetre. As a result of the individually differing thickness of the blanks and due to the volume constancy of the material to be worked, considerable geometrical differences, particularly length differences occur on the manufactured part. It is therefore necessary to use further machining steps, particularly finishing by cutting. This leads to a considerable rise in the machine, personnel, time and material costs and therefore the costs of the finished precision components.
The object of the invention is to provide a method and an apparatus enabling the manufacture of particularly high precision workpieces.
This object is achieved by a method having the features of claim 1 and an apparatus having the features of claim 10.
Preferred further developments of the method according to the invention and advantageous embodiments of the apparatus according to the invention are claimed in the subclaims.
According to the invention, a method of the aforementioned type is further developed in that for compensating dimensional variations of the blank at least one compensating area is formed into the workpiece, that before and/or during flow-forming geometrical data of the blank and/or workpiece are determined with a measuring device, that for obtaining a desired final geometry of the workpiece the geometrical parameters of the at least one compensating area are individually calculated as a function of the geometrical data determined and that by means of a control device the infeeding of the flow-forming roll is controlled in accordance with the calculated geometrical parameters of the compensating area, so that independently of dimensional variations of the blank it is possible to form a workpiece having the desired final geometry.
The essence of the invention is that, as a function of the specifically existing dimensional variation, each blank is individually manufactured. For this purpose, according to the invention, before and/or during flow-forming specific geometrical data of the blank and/or workpiece are determined. On the basis of said geometrical data an individual compensating area is then worked into the workpiece. This can bring about the decisive advantage that, independently of any dimensional variations of the blank, the workpiece always has a desired final geometry.
Another important advantage is that with the method according to the invention it is possible to manufacture workpieces with such a high precision, that there is no need for subsequent machining steps, particularly cutting finishing operations. This permits significant savings in time, personnel and machine costs.
According to a preferred development of the method, the at least one compensating area is worked into an area of the workpiece not critical for the functionality thereof. This can bring about the advantage that the functionality of workpieces is maintained, independently of how the compensating area is in each case individually formed.
As geometrical data preferably at least one axial length of the blank and/or workpiece is determined, particularly several times. As the workpiece wall thickness on rolling out is usually significantly reduced, i.e. the workpiece is significantly lengthened, the axial length is sensitively dependent on any blank dimensional variations present, so that as a result of this quantity the geometrical parameters of the compensating area can be very precisely determined.
With the aid of suitable path measuring systems, whose measured data are processed by a main frame computer, according to the invention it is possible to control wall thickness tolerances occurring during the manufacturing process.
As geometrical data it is also possible to determine a diameter and/or a wall thickness of the blank and/or workpiece. This makes it possible to increase the precision of determining the parameters of the compensating area.
Besides the geometrical data further measurements can be performed on the blank and/or workpiece. For example, before, during and/or after flow-forming a workpiece temperature can be determined.
In addition, during flow-forming, it is possible to determine a pressure in the workpiece, particularly in the axial direction.
The specific geometry of the workpiece is sensitively dependent on the pressure and temperature, so that a recording of these parameters allows a further increase in the precision of manufacture.
Preferably the temperature and/or pressure determined are supplied to the computer means and are included in the calculation of the geometrical parameters of the compensating area.
In a preferred variant of the method according to the invention, the compensating area is formed as a cylindrical area and/or as at least one bevelled area. These forms can firstly be produced in a simple manner on a flow-forming machine and in addition the geometrical parameters of these forms can be calculated particularly easily.
As a function of the workpiece design, it is possible to implement other, randomly shaped compensating areas.
If the dimensional variations of the blank are particularly large, it is possible to work several compensating areas into the workpiece. This can also be advantageous if it is desired that the variation between the geometrical parameters of a compensating area between individual workpieces is not to be too large.
The method according to the invention can be performed as down-feed and also up-feed methods.
An apparatus of the aforementioned type is inventively further developed in that at least one measuring device is provided for determining the geometrical data of the workpiece, that the measuring device is linked to a computer means, which is designed for calculating the geometrical parameters of a compensating area, which is worked into the workpiece for individually compensating dimensional variations of the blank and that by means of the control device the infeed of the flow-forming roll is controllable, so that the compensating area of the workpiece is constructed as a function of the geometrical parameters individually calculated by the computer means.
The apparatus, which can also be referred to as a flow-forming machine, can be operated in path-controlled and/or pressure-controlled manner. With the aid of NC technology, it is possible to implement path-giving flow-forming operations and the exact positioning of the flow-forming rolls in the longitudinal and transverse axis.
The measuring device preferably has at least one displacement transducer. These can be of an optical or acoustic nature and/or in the form of a sensor for determining the electrical conductivity.
In an advantageous development of the inventive apparatus several displacement transducers are provided and are in particular arranged in axially spaced manner. This advantageously allows a multiple determination, e.g. of an axial length of the workpiece during the flow-forming method.
In order to increase the information base for calculating the geometrical parameters of the compensating area, it is also possible for the measuring device to have a sensor for determining the diameter of the workpiece and/or a wall thickness of the workpiece.
In addition, measuring devices or sensors can be provided for determining further physical quantities, so that the workpiece can be even more precisely characterized and the manufacturing process can be performed under even better defined conditions.
For example, for determining a temperature of the workpiece, it is possible to provide a temperature sensor, or for determining a pressure in the workpiece, particularly in an axial direction, a pressure sensor can be provided.